Can we use "any" with singular countable nouns? If so, what's the grammar rule? Can you share a link or a source so that I could refer ?
Ex-
01. There isn’t any issue.
02. There isn’t any student in the class?
03. Isn’t there any student in the class?
Are the above ssentences correct?
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The site seems to contradict itself. First, it says "Do not use any' with singular countable nouns. It then says "It's more common to use 'isn't+a' for singular countable nouns".
There might be some truth to their second assertion; there isn't any reason to believe the first.
Yes, you can, and your examples are acceptable.
The three main uses are
[1] I haven't got any job lined up for you today, I'm afraid.
[2] I don't think any candidate expressed a view on this point.
[3] Any policeman will be able to help you.
You may encounter the terms 'non-proportional' to describe the sense of "any" in [1], 'proportional' for that in [2] and 'free choice' for that in [3].
Note that the count singular use in [1] is relatively rare.
I quickly tried to find a suitable resource on the 'Net, but they all said the same as the the one you cited.